refactor(dsl): use traits instead of enums

dsl/src/dsl_conv.rs

@@ -0,0 +1,51 @@
+use crate::*;
+
+/// `T` + [Dsl] -> `Self`.
+pub trait FromDsl<T>: Sized {
+    fn from_dsl (state: &T, dsl: &impl Dsl) -> Perhaps<Self>;
+    fn from_dsl_or (state: &T, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<Self> {
+        Self::from_dsl(state, dsl)?.ok_or(err)
+    }
+    fn from_dsl_or_else (state: &T, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<Self> {
+        Self::from_dsl(state, dsl)?.ok_or_else(err)
+    }
+}
+
+impl<'s, T: FromDsl<U>, U> DslInto<'s, T> for U {
+    fn dsl_into (&self, dsl: &impl Dsl) -> Perhaps<T> {
+        T::from_dsl(self, dsl)
+    }
+}
+
+/// `self` + [Dsl] -> `T`
+pub trait DslInto<'s, T> {
+    fn dsl_into (&'s self, dsl: &impl Dsl) -> Perhaps<T>;
+    fn dsl_into_or (&'s self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<T> {
+        self.dsl_into(dsl)?.ok_or(err)
+    }
+    fn dsl_into_or_else (&'s self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<T> {
+        self.dsl_into(dsl)?.ok_or_else(err)
+    }
+}
+
+/// `self` + `T` + -> [Dsl]
+pub trait IntoDsl<T> {
+    fn into_dsl (&self, state: &T) -> Perhaps<impl Dsl>;
+    fn into_dsl_or (&self, state: &T, err: Box<dyn Error>) -> Usually<impl Dsl> {
+        self.into_dsl(state)?.ok_or(err)
+    }
+    fn into_dsl_or_else (&self, state: &T, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
+        self.into_dsl(state)?.ok_or_else(err)
+    }
+}
+
+/// `self` + `T` -> [Dsl]
+pub trait DslFrom<T> {
+    fn dsl_from (&self, dsl: &impl Dsl) -> Perhaps<impl Dsl>;
+    fn dsl_from_or (&self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or(err)
+    }
+    fn dsl_from_or_else (&self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or_else(err)
+    }
+}